Core Framework & Diagram Protein and Immunity

As a way to supplement insufficient real food protein, protein powders are useful. Whey protein is rich in branched-chain amino acids and cysteine, and contains some immunomodulatory whey protein fractions (like lactoferrin, α-lactalbumin). But it's a supplementary means, not a replacement — real food contains other immune-related nutrients (zinc, iron, B vitamins, etc.) that protein powder lacks.

In individuals with normal kidney function, 1.0–2.0 g/kg/day protein intake — current evidence does not support harming kidney function. Kidney disease patients (with decreased glomerular filtration rate) do need to restrict protein, but this is for conditions with pathological basis, not applicable to ordinary people. If you have a kidney disease history, consult a nephrologist before deciding on intake.

During acute infection, the immune system's protein needs rise while appetite often falls. Short-term (three to five days) insufficient intake has the body mobilizing muscle protein (breaking down muscle protein to supply amino acids) to sustain the immune response — a normal physiological coping mechanism. But if infection continues longer, or baseline protein reserves are already insufficient (sarcopenic older adults), this compensation mechanism has limited capacity and significantly affects prognosis. Ingesting protein as soon as able to tolerate is meaningful.

A well-designed vegetarian diet doesn't necessarily lead to immune function decline. Key factors: whether total protein quantity is adequate (through diverse food combinations), and whether possibly deficient nutrients are supplemented (vitamin B12, iron, zinc, omega-3 fatty acids, vitamin D). A poorly designed vegetarian diet (over-relying on refined staples, single protein sources) may show multiple simultaneous immune-related nutritional deficiencies.